# Using Docker Images

Deis supports deploying applications via an existing [Docker Image][].
This is useful for integrating Deis into Docker-based CI/CD pipelines.


## Prepare an Application

Start by cloning an example application:

    $ git clone https://github.com/deis/example-go.git
    $ cd example-go
    $ git checkout docker

Next use your local `docker` client to build the image and push
it to [DockerHub][].

    $ docker build -t <username>/example-go .
    $ docker push <username>/example-go


### Docker Image Requirements

In order to deploy Docker images, they must conform to the following requirements:

* The Dockerfile must use the `EXPOSE` directive to expose exactly one port.
* That port must be listening for an HTTP connection.
* The Dockerfile must use the `CMD` directive to define the default process that will run within the container.


## Create an Application

Use `deis create` to create an application on the [controller][].

    $ mkdir -p /tmp/example-go && cd /tmp/example-go
    $ deis create
    Creating application... done, created example-go

!!! note
    The `deis` client uses the name of the current directory as the
    default app name.


## Deploy the Application

Use `deis pull` to deploy your application from [DockerHub][] or
a public registry.

    $ deis pull gabrtv/example-go:latest
    Creating build...  done, v2

    $ curl -s http://example-go.local3.deisapp.com
    Powered by Deis

Because you are deploying a Docker image, the `cmd` process type is automatically scaled to 1 on first deploy.

Use `deis scale cmd=3` to increase `cmd` processes to 3, for example. Scaling a
process type directly changes the number of [Containers][container]
running that process.

!!! attention
    Support for Docker registry authentication is coming soon.


[container]: ../reference-guide/terms.md#container
[controller]: ../understanding-workflow/components.md#controller
[Docker Image]: https://docs.docker.com/introduction/understanding-docker/
[DockerHub]: https://registry.hub.docker.com/
[CMD instruction]: https://docs.docker.com/reference/builder/#cmd